Since installing Premiere Pro CS6, I can't create any titles. When I choose Title > New Title > any of the options listed, the titling interface opens, but it keeps churning and won't let me enter text, etc. Eventually I have to force quit. Has this happened to anyone else? Titles worked fine for me in CS5.5.

One of the most common issues with PrPro's Titler is corrupt, or poorly-written fonts. I would look into that, to either solve the issue, or get fonts out of the way early. This article goes into more detail on fonts and Titler (plus some other Adobe programs): http://forums.adobe.com/message/2186476#2186476

Also, John T's request for more info will be helpful, especially if you do not have a font issue.

The Titler is little more than a floating frame containing a particular set of panels. There's no reason you can't leave it open when you're done creating/editing Title A, then eventually go File>New>Title. When you click OK in New Title, the Titler shows the blank slate for Title B, with aspect ratio adjusted if applicable.

I hit OK in the Titler dialog box and the actual Titler interface comes up, but it won't let me enter text, images or anything; it just churns until I have to force quit PP. The Titler dialog box and the Titler interface are open simultaneously during both actions. It seems like the program is hanging somewere between the two actions. I can post a video if this will help.

No need. Normally the dialog closes when the titler opens. That it's not suggests something went weird with your install. Try deactivating, uninstalling, running the Clean Script tool, and then reinstalling.